Flakes with undulate borders and method of forming thereof

ABSTRACT

The invention provides a plurality of substantially same planar pigment flakes, each formed of one or more thin film layers. Each flake has a face surface and a flake border delimiting the face surface; the flake border undulates in the plane of the flake. The flakes have a pre-selected shape, may have a symbol or a grating thereon. A method of manufacturing of these flakes including the steps of: (a) providing a substrate having a plurality of one-flake regions and a plurality of depressions or protrusions disposed therebetween and not extending into the one-flake regions, (b) coating the substrate with a releasable coating, and (c) removing the releasable coating and breaking it into the flakes; wherein two adjacent of the one-flake regions are separated by at least three of the depressions or protrusions for facilitating the breaking of the releasable coating into the flakes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation-in-part of U.S. patentapplication Ser. No. 11/243,122 filed Oct. 4, 2005, now publishedapplication 2006/0035080, which is a continuation-in-part of U.S. patentapplication Ser. No. 10/762,158 filed Jan. 20, 2004, now issued U.S.Pat. No. 7,241,489, which is a continuation-in-part of U.S. patentapplication Ser. No. 10/641,695 filed Aug. 14, 2003, now issued U.S.Pat. No. 7,258,915, and also is a continuation-in-part of U.S. patentapplication Ser. No. 10/243,111 filed Sep. 13, 2002, now issued U.S.Pat. No. 6,902,807, the disclosures of which are incorporated herein byreference for all purposes. The U.S. patent application Ser. No.11/243,122 also claims priority from U.S. provisional patent applicationNo. 60/696,593 filed Jul. 5, 2005, which is incorporated herein byreference. The present application claims priority from U.S. provisionalpatent application No. 61/051,463 filed May 8, 2008, which isincorporated herein by reference for all purposes.

TECHNICAL FIELD

The present invention relates generally to thin-film pigment flakes, andmore particularly to a method of manufacturing of shaped flakes.

BACKGROUND OF THE INVENTION

Specialty pigments are used in a variety of security applications, suchas anti-counterfeiting devices printed on banknotes, packaging ofhigh-value items, seals for containers, etc. One type of specialtypigments is color-shifting flakes used in special-effect inks. Thecolor-shifting flakes are manufactured by deposition of several layersof various materials onto a substrate and then breaking the depositedcoating into single flakes. This method results in irregularly-shapedpigment flakes.

Alternatively, flakes of a particular shape provide a security featurewhich is visible only under magnification. Additionally, shaped flakesmay be used for coding of security inks or any other objects. Anotheranti-counterfeiting approach uses microscopic symbols, for example,embossed on the pigment flakes. A combination of the above features maybe used in the same flakes for enhanced security.

SUMMARY OF THE INVENTION

The invention relates to a method of manufacturing of pigment flakesincluding the steps of: (a) providing a substrate having a plurality ofone-flake regions and a plurality of depressions or protrusions disposedtherebetween and not extending into the one-flake regions, (b) coatingthe substrate with a releasable coating, and (c) removing the releasablecoating and breaking it into the flakes; wherein two adjacent of theone-flake regions are separated by at least three of the depressions orprotrusions for facilitating the breaking of the releasable coating intothe flakes.

The invention provides a plurality of substantially same planar pigmentflakes. Each flake includes one or more thin film layers and has a facesurface and a flake border delimiting the face surface. A diameter ofthe face surface is less than 100 microns and a thickness of the flakeis less than 4 microns; the flake border undulates in the plane of theflake.

Another aspect of the present invention relates to a method ofmanufacturing of pigment flakes wherein a substrate has polygon-shapedone-flake regions with a number of sides between 3 and 6, and one or tworows of depressions or protrusions between two adjacent one-flakeregions for forming a perforation line. The number of the depressions orprotrusions per one side of the polygon-shaped one-flake regions isbetween 7 and 20.

The invention further provides a plurality of substantially same planarpigment flakes, wherein the each flake includes one or more thin filmlayers and has a face surface and a flake border delimiting the facesurface. A diameter of the face surface is less than 100 microns and athickness of the flake is less than 4 microns. Each flake has a squareshape with at least three sides thereof being undulate lines in theplane of the flake, wherein each line undulates periodically and has anumber of waves between 8 and 20 per side of the polygon.

Another feature of the present invention provides shaped pigment flakeswith a symbol thereon and an undulate border. The invention provides amethod of forming such flakes using a substrate with same-shapedone-flake regions separated by depressions or protrusions forfacilitating breakage of the flakes along the undulate lines; theone-flake regions have the symbols formed therein.

Yet another aspect of this invention provides shaped grated flakes aswell as a method of forming such flakes using a substrate withpolygon-shaped one-flake regions which have grooves or ridges forproviding a grating to the flakes, wherein the grooves or ridges of afirst one-flake region are separated from the grooves or ridges of asecond one-flake region by one or two rows of depressions orprotrusions.

The invention also provides a sheet of one-flake regions, for formingthe flakes defined in claim 1. The sheet has (a) a substrate having theone-flake regions and a plurality of depressions or protrusions disposedtherebetween and not extending into the one-flake regions, and (b) areleasable coating coated onto the substrate, wherein a diameter of theone-flake regions is less than 100 microns and stripes of depressionsand protrusions between two of the one-flake regions have a width ofless than 20% of the diameter, and wherein two adjacent of the one-flakeregions are separated by at least three of the depressions orprotrusions for facilitating the breaking of the releasable coating intothe flakes, so that breakage is likely to occur about the depressions orprotrusions, when the releasable coating is separated into the flakes.

According to the invention, a plurality of substantially same pigmentflakes is provided, wherein each flake has one or more thin film layers,a diameter of the flake is between 2 and 100 microns, and a thickness ofthe flake is less than 50% of the flake diameter, the flake border is anundulate line in the plane of the flake and has at least four waves perside of the flake.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in greater detail with reference to theaccompanying drawings, wherein:

FIG. 1 is a micro photograph of a flake in accordance with theinvention;

FIG. 2 is a schematic plan view of a deposition substrate in accordancewith one embodiment of the invention;

FIG. 3 is a schematic plan view in accordance with one embodiment of theinvention;

FIG. 4 is a perspective view of the substrate shown in FIG. 3;

FIG. 5A is a schematic plan view of a deposition substrate formanufacturing flakes with symbols;

FIG. 5B is a schematic plan view of a deposition substrate formanufacturing grated flakes;

FIG. 6A is a schematic plan view of a pigment flake;

FIG. 6B is a micro photograph of flakes with undulate borders;

FIG. 7 is a schematic plan view of a pigment flake with a symbol;

FIG. 8 is a schematic plan view of a pigment flake with a diffractiongrating; and,

FIG. 9 is a perspective view of a sheet of one-flake regions formingflakes with undulate borders.

DETAILED DESCRIPTION

The method described below provides pigment flakes with a postagestamp-like edge for easy severing along the designated lines during themanufacturing process. The perforation is enabled by using a particularstructured deposition substrate which has teeth (protrusions) or holes(depressions) between one-flake regions. Portions of the flake materialdeposited into the holes or on top of the teeth easily break from theflake portions and from each other, thus creating flakes of a desiredshape and debris fragments of a significantly size smaller than theflakes. FIG. 1 illustrates such a flake; small debris fragments arevisible in the top right corner of the picture.

With reference to FIG. 2, a substrate 100 has a plurality of one-flakeregions 110 and depressions or protrusions 120 disposed between theone-flake regions 110. The substrate 100 is designed for manufacturingof postage-stamp shaped flakes, wherein perforation between the flakesis formed by the depressions or protrusions 120.

The one-flake regions 110 have a shape selected for the flakes beingmanufactured. FIG. 2 shows the one-flake regions 110 to have a squareshape; however, they may have other shapes, such as a circle or apolygon with 3 or 6 sides. The largest dimension of the one-flake region110, a diameter 145, depends on the desired flake size, and is greaterthan 2 and less than 100 microns.

A strip of depressions and protrusions 120 between two of the one-flakeregions 110 have a width of less than 20% of the diameter 145. In FIG.2, the depressions or protrusions 120 form rows 130 so that one row 130separates a pair of adjacent one-flake regions 110.

Breaking features 120 may be either depressions, or protrusions, or amixture thereof. The depressions and protrusions 120 may be from 100 nmto 2000 nm deep or high, respectively.

The density of the depressions or protrusions 120 depends on the flakesize; two adjacent one-flake regions 110 are separated by at least threedepressions or protrusions 120 for facilitating the breaking of thereleasable coating into the flakes. Preferably, the substrate 100 hasfrom 7 to 20 depressions/protrusions 120 per a flake side.

By way of example, a substrate for manufacturing of 2×2 microns flakeshas the depressions/protrusions 120 of about 0.1-0.2 microns indiameter, and a substrate for manufacturing of 25×25 microns flakes hasthe depressions/protrusions 120 of about 1.5-2.5 microns in diameter.

In another example, for manufacturing of 15×15 microns square-shapedflakes shown in FIG. 6B, a substrate has a distance 140 between twoneighboring strips of the depressions/protrusions 120, which arerepresented by rows 130, equal to 15 microns; the rows 130 include 7holes per a 15-microns interval thus causing a side of the flake to have7 waves.

The depressions and protrusions 120 are preferably round in the plane ofthe substrate so as to minimize the size of debris fragments for a givenseparation of the flakes; however the depressions/protrusions 120 mayhave any shape.

The depressions or protrusions 120 may be directly adjacent to oneanother or separated by an isthmus so as to guarantee separation of thedebris into the smallest fragments when the flakes are released from thesubstrate.

With reference to FIG. 3, the depressions/protrusions 120 between twoone-flake regions 110 may be arranged in a zigzag pattern 121 formingtwo rows 170 to ensure better separation of the debris fragmentsassociated with single depressions or protrusions 120.

By way of example, FIG. 4 is a microphotograph of a portion of asubstrate with two rows of depressions arranged in the zigzag pattern.The substrate is made by embossing a plastic film with a nickel shim.

Since the depressions or protrusions 120 are for breaking the one-flakeregions 110 from one another, the depressions or protrusions 120 are notextending into the one-flake regions 110.

With reference to FIG. 5A, the one-flake regions 110 may have one ormore symbols 150 embossed in the surface of the substrate 100 orprotruding therefrom. The symbols 150 are understood to includealpha-numeric symbols, as well as logos, barcodes, etc.

With reference to FIG. 5B, the one-flake regions 110 may have grooves orridges 160 for providing a grating structure to the flakes. The groovesor ridges 160 extend through the one-flake region 110 and the grooves orridges 160 of one region 110 are separated from the grooves or ridges ofanother region 100 by a row of the depressions or protrusions 120, or bytwo rows, or by a strip of irregularly positioned depressions orprotrusions 120. The grooves or ridges 160 may be spatially separatedfrom the depressions or protrusions 120 by isthmuses as shown in FIG.5B, or be in direct contact with the depressions or protrusions 120. Thegrooves or ridges 160 have a frequency in the range of from 100 to 5000lines/mm.

Alternatively, the substrate 100 shown in FIG. 5B may have only the rowsof the depressions or protrusions 120 which are orthogonal to thegrooves or ridges 160. In that case, the releasable coating would breakalong the grooves or ridges 160 in one direction and along the rows 130in another direction.

Deposition of a releasable coating onto the substrate 100 shown in FIG.5B, subsequent removal of the coating and its breakage about thedepressions/protrusions 120, result in diffractive flakes having a samepre-selected shape. Such flakes have their borders undulate in the planeof the flake, whereas conventional diffractive flakes, broken acrosstheir grooves, have an irregular shape and a flake border undulateup-and-down relative to the plane of the flake.

For the diffractive flakes, as well as for all the flakes of the instantinvention, the in-plane undulate flake border is a result of the novelmanufacturing process, which provides flakes of a preselected shape withvery low quantity of debris and debris fragments of a smaller size thanother methods. Additionally, the in-plane undulate flake borders providea security feature, which is difficult to counterfeit and simple todetect.

The substrate 100 may be formed of any material; however, plasticsubstrates, e.g. formed of polyethylene terephthalate (PET), arepreferable.

The origination of the master for the fabrication of surface-reliefmicrostructures for the structured substrate 100 may be fabricated usingknown techniques, such as laser writing, e-beam writing, diamondscribing, masking, etc. The methods of laser and e-beam direct writingare better suited when a fine microstructure is desired. After theoriginal master is originated, a nickel shim is electroformed andrecombined to get the final production Ni shim to a size desired inproduction. The nickel shim may be used in any of high resolutionreplication technologies, such as hot stamping, embossing, hot-rollerembossing, injection-molding, UV casting-embossing, etc. In massproduction of pigment flakes, the embossed substrate is a long roll ofplastic foil, and the replication technology is UV casting orpressure/temperature embossing.

In the process of flake manufacturing, the substrate 100 is coated withone or more thin film layers forming a releasable coating. Usually afirst layer of the releasable coating is a release layer, by way ofexample, made of a water-soluble material. In some cases, themicrostructured layer itself can be soluble so that the release layer isnot necessary.

A roll coater is one type of apparatus, which may be used to produceflakes according to embodiments of the invention. A roll of polymersubstrate material is passed through a deposition zone(s) and coatedwith one or more thin film layers, which are typically 50 to 3000 nmthick layers of inorganic material; however organic layers also may bepresent. Multiple passes of the roll of polymer substrate back and forththrough the deposition zone(s) may be made. Known deposition techniquesinclude variations of chemical vapor deposition (CVD) and physical vapordeposition (PVD) methods. The releasable coating is then removed fromthe polymer substrate and broken into flakes. In more detail thisprocess is described in U.S. Pat. No. 5,059,245, incorporated herein byreference.

By way of example, the releasable coating includes a reflector layer, anabsorber layer, and a spacer layer therebetween, for manufacturing ofcolor-shifting pigment flakes. Preferable materials are Aluminum, MgF₂,and Chromium as described in the U.S. Pat. No. 5,059,245. Alternatively,the releasable coating is formed of one or more transparent orsemi-transparent materials for manufacturing covert flakes for securityapplications as described in U.S. Pat. No. 7,258,915, incorporatedherein by reference. Further, the releasable coating may include a metallayer for providing bright reflective flakes and/or a layer of magneticmaterial for orientation of the flakes in a magnetic field as describedin U.S. Pat. No. 6,150,022, incorporated herein by reference. Thereleasable coating has a thickness in the range of from 100 nm to 4000nm.

The substrate 100 has a microstructure that facilitates breaking of theflakes in specific shapes during the post-processing steps. These stepsinclude stripping off the coating from the substrate 100 andgrinding/sizing the stripped material. Also, in the printingapplication, some of the printing processes include the application offorces that tend to further break the flakes from each other.

One of the flakes manufactured as described above is schematically shownin FIG. 6A. The flake 300 has a face surface 310 and a flake border 330,which delimits the face surface 310. The flake 300 is formed of the oneor more thin film layers discussed above. A diameter 320 of the facesurface 310 is less than 100 microns which corresponds to the diameter145 of the one-flake region 110 shown in FIGS. 2, 3, 5A and 5B. Athickness of the flake 300 is less than 50% of the diameter 320 so as toensure planar characteristics of the flake. The flake 300 has a planarcentral region 340.

By way of example, FIG. 6B is a microphotograph of flakes similar to theflake 300 shown in FIG. 6A. The square flakes shown in FIG. 6B have aflake border with 7 waves per 15-microns side of the square.

Optionally, the flake 300, shown as flake 301 in FIG. 7, has one or moresymbols 350 thereon, which correspond to the symbols 150 on thesubstrate 100 shown in FIG. 5A.

Optionally, the flake 300, shown as flake 302 in FIG. 8, has adiffraction grating 360 formed on the grooves or ridges 160 of thesubstrate 100 shown in FIG. 5B. It should be noted that the grating 360and the grooves or ridges 160 are depicted not to scale for illustrationpurposes.

According to the instant invention, the flake border 330 shown in FIGS.6-8 undulates in the plane of the flake.

The shaped pigment flakes of the instant invention, such as shown inFIGS. 1, 6A, 6B, 7 and 8, may be color-shifting flakes, brightreflective flakes, transparent or semi-transparent flakes, may include amagnetic material and/or have symbols thereon; the flakes may includemultiple layers or be single-layer flakes, e.g. made of a metal or atransparent material. The flakes of the instant invention have adiameter between 2 and 100 microns and a thickness of from 100 nm to4000 nm. The aspect ratio of flake diameter to flake thickness is atleast 2 to 1 and preferably higher.

The pigment flakes formed by the method of the instant invention mayhave any preselected shape; however the polygon shapes are preferredbecause of easier perforation along the straight lines. Since at leastsome of the sides of the flakes are not straight but wavy (undulate)lines, the shape of the flakes is better described as a substantiallypolygonal shape.

The preferable number of sides in the polygon-shaped flakes is 3, 4 or6, in order to ensure full utilization of the substrate surface.Preferably all the sides of the flakes are undulate lines; it isdesirable for flakes to have at least three undulate sides.

In one embodiment, at least a portion of the flake border 330 undulatesperiodically and has at least four waves. With reference to FIG. 9, anamplitude 410 of the waves is less than 20% of the diameter 320 of theface surface 310.

In practice, the undulate flake border is not necessarily an idealpostage-stamp-like border as shown e.g. in FIG. 6A. Some of the debrisformed over the depressions or protrusions 120 may be still attached tothe flake as it is shown in FIG. 1; all the border of the flake shown inFIG. 1 is an undulate line.

FIG. 9 shows a sheet 400 of one-flake regions 310 for forming the flakes300, 301, or 302. The sheet 400 includes the substrate 100, not shown inFIG. 9, but shown in FIGS. 2-5B. Supported by the substrate 100 is areleasable coating 430 formed of the one or more thin film layersdescribed above. The structural features of the substrate 100 arereplicated in the coating 430. The substrate 100 and the coating 430have the one-flake regions 110/310 and the depressions or protrusions120 disposed therebetween and not extending into the one-flake regions110/310. The diameter 145/320 of the one-flake regions is in the rangeof from 2 to 100 microns; and stripes 420 of the depressions orprotrusions 120 between two of the one-flake regions 110/310 have awidth of less than 20% of the diameter 145/320. Two adjacent one-flakeregions 110/310 are separated by at least three depressions orprotrusions 120 for facilitating the breakage of the releasable coating430 into the flakes 300, 301 or 302, so that breakage is likely to occurabout the depressions or protrusions 120, when the releasable coating430 is separated into the flakes. At least some of the one-flake regions110/310 may have symbols 150/350 or diffraction grating 160/360. Thecoating 430 may be the color-shifting coating or any other coatingdescribed above.

Advantageously, the method of the instant invention creates less debrisand of a smaller size than other known methods. The debris are lessvisually apparent and less likely to be mistaken for broken flakesbecause of the size difference. Further, the undulate borders of theflakes make counterfeiting more difficult and provide an additionalproduct-authentication feature.

The shaped flakes can have other than optical applications. For example,specifically shaped thin flakes can carry drugs, e.g. by inhalation, toa particular part of the body; considering that a 8 micron shaped flakehas dimensions close to those of blood cells. Alternatively,specifically microstructured shapes and the materials applied can beengineered to have high surface areas for catalysis purposes.

1. A plurality of substantially same planar pigment flakes, each flakecomprising one or more thin film layers, each fake having a face surfaceand a flake border delimiting the face surface, wherein a diameter ofthe face surface is less than 100 microns and a thickness of the flakeis less than 4 microns, and wherein the flake border undulates in theplane of the flake.
 2. The flakes as defined in claim 1, wherein eachflake has a substantially polygon shape and at least three sides of thepolygon are undulate lines.
 3. The flakes as defined in claim 2, whereinthe undulate lines each comprises at least four waves and wherein anamplitude of the waves is less than 20% of the diameter of the facesurface.
 4. The flakes as defined in claim 3, wherein the undulate linesundulate periodically.
 5. The flakes as defined in claim 4, wherein thepolygon is a square and the undulate lines have a number of wavesbetween 7 and 20 per side of the polygon.
 6. The flakes as defined inclaim 4, wherein each flake comprises a symbol.
 7. The flakes as definedin claim 4, wherein each flake comprises a diffraction grating.
 8. Theflakes as defined in claim 4, wherein the one or more thin film layerscomprise a reflector layer, an absorber layer, and a spacer layertherebetween, for providing a color-shifting effect to the flakes.
 9. Amethod of manufacturing of pigment flakes comprising the steps of: (a)providing a substrate having a plurality of one-flake regions and aplurality of depressions or protrusions disposed therebetween and notextending into the one-flake regions, (b) coating the substrate with areleasable coating, and (c) removing the releasable coating and breakingit into the flakes; wherein two adjacent of the one-flake regions areseparated by at least three of the depressions or protrusions forfacilitating the breaking of the releasable coating into the flakes. 10.The method as defined in claim 9, wherein a diameter of the one-flakeregions is in the range of from 2 to 100 microns and stripes ofdepressions and protrusions between two of the one-flake regions have awidth of less than 20% of the diameter.
 11. The method as defined inclaim 10, wherein the one-flake regions are polygon-shaped regions witha number of sides between 3 and
 6. 12. The method as defined in claim11, wherein the depressions or protrusions are arranged in one or tworows separating adjacent one-flake regions for forming a perforationline.
 13. The method as defined in claim 12, wherein a number of thedepressions or protrusions per one side of the polygon-shaped one-flakeregions is between 7 and
 20. 14. The method as defined in claim 12,wherein two of the adjacent one-flake regions are separated by two rowsof the depressions or protrusions arranged in a zigzag pattern.
 15. Themethod as defined in claim 11, wherein at least some of the one-flakeregions have a symbol thereon.
 16. The method as defined in claim 12,wherein at least some of the one-flake regions have grooves or ridgesfor providing a grating to the flakes, wherein the grooves or ridges ofa first of the one-flake regions are separated from the grooves orridges of a second of the one-flake regions by the one or two rows ofthe depressions or protrusions.
 17. The method as defined in claim 12,wherein the releasable coating comprises a reflector layer, an absorberlayer, and a spacer layer therebetween, and wherein the flakes arecolor-shifting pigment flakes.
 18. The method as defined in claim 12,wherein the releasable coating has a thickness in the range of from 100nm to 4000 nm.
 19. A plurality of flakes manufactured by the methoddefined in claim
 13. 20. A sheet of one-flake regions, for forming theflakes defined in claim 1, comprising: (a) a substrate having theone-flake regions and a plurality of depressions or protrusions disposedtherebetween and not extending into the one-flake regions, and (b) areleasable coating coated onto the substrate, wherein a diameter of theone-flake regions is less than 100 microns and stripes of depressionsand protrusions between two of the one-flake regions have a width ofless than 20% of the diameter, and wherein two adjacent of the one-flakeregions are separated by at least three of the depressions orprotrusions for facilitating the breaking of the releasable coating intothe flakes, so that breakage is likely to occur about the depressions orprotrusions, when the releasable coating is separated into the flakes.21. The sheet as defined in claim 20, wherein the releasable coating isa color-shifting coating.
 22. The sheet as defined in claim 21, whereinat least some of the one-flake regions comprise symbols.